music: do not auto-index unless indeterminate

Make IndexerService only auto-index music when there is no library AND
no loading has occured.

This resolves an issue where if IndexerService dies after a failed
index, IndexerService would try to index music regardless, as there was
no library present.

app/src/main/java/org/oxycblt/auxio/music/Indexer.kt

@@ -61,6 +61,13 @@ class Indexer {
     private var currentGeneration = 0L
     private val callbacks = mutableListOf<Callback>()
 
+    /**
+     * Whether this instance is in an indeterminate state or not, where nothing has been previously
+     * loaded, yet no loading is going on.
+     */
+    val isIndeterminate: Boolean
+        get() = lastResponse == null && loadingState == null
+
     fun addCallback(callback: Callback) {
         val currentState =
             loadingState?.let { State.Loading(it) } ?: lastResponse?.let { State.Complete(it) }

app/src/main/java/org/oxycblt/auxio/music/IndexerService.kt

@@ -62,10 +62,9 @@ class IndexerService : Service(), Indexer.Callback {
 
         notification = IndexerNotification(this)
 
-        // FIXME: Do not re-index if Indexer has already completed
         indexer.addCallback(this)
-        if (musicStore.library == null) {
+        if (musicStore.library == null && indexer.isIndeterminate) {
-            logD("No library present, loading music now")
+            logD("No library present and no previous response, loading music now")
             onRequestReindex()
         }